Organic EL elements are extremely susceptible to moisture and the like, and in order to ensure a satisfactory lifespan for an organic EL element, the organic EL element must be isolated and protected from atmospheric moisture and the like. As a result, a step known as sealing is essential in the production of organic EL panels.
In a conventional sealing step, a encapsulation substrate such as a metal cap or a sealing glass having an internal space provided therein is used to form an airtight seal at a sealing portion. A desiccant or drying sheet which adsorbs moisture is housed inside the internal space, and absorbs any moisture or the like which permeates through the peripheral sealing portion. This sealing method is also known as hollow sealing, and is applicable to small organic EL elements.
However, if hollow sealing is applied to a large organic EL element, then a problem arises in that the encapsulation substrate may contact the organic EL element within the hollow portion, thereby damaging the organic EL element.
Further, in the case of organic EL elements used for illumination, a large amount of heat is generated during light emission, and the internal temperature of the panel increases. As a result, uneven brightness occurs due to a temperature distribution across the panel surface, and in the worst case, thermal runaway can result in element failure. Moreover, another problem is that the increase in the panel temperature accelerates deterioration in the brightness of the organic EL element, resulting in a shortening of the operating life. Accordingly, an entirely solid sealing technique which does not have an internal sealed space is required.
Hence, there is a need for a sealing method which, even for large panels, can protect the organic EL element from atmospheric moisture to ensure a good lifespan, while also ensuring there is no contact between the element substrate and the encapsulation substrate, and a sealing method which can transmit heat to both the element substrate and the encapsulation substrate, enabling heat dissipation and uniform heating. In order to address the above problems, a method has been proposed in which a filler is disposed between the element substrate and the encapsulation substrate (see Patent Document 1).
In Patent Document 1, a sealant is disposed around the outermost periphery of the element on the element substrate, a desiccant is provided inside the sealant, and a filler is disposed on top of the element. A encapsulation substrate is positioned facing the element substrate, the two substrates are pressure welded under reduced pressure, and the sealant is then cured.